Just reading this so apologies for the delay.
We have the same boiler and the exact same thing is happening. Its got that bad now i am topping it up daily else the heating/water isnt coming on. Plumber came round last week and showed me where the problem was. Its basically leaking, you can see the drip of water going into the condensation filter thing, which is then pushed outside. Hence why we were not seeing a pool of water where the leak is. He has told us this is quite a common fault with this boiler. It is repairable BUT its a full strip & not cheap and since its not that new anymore, have decided on a new boiler.